Differentiated products that make use of characteristics provided by synthetic fibers which are generally termed new synthetic fibers are formed by composite finishing of original yarns having individual properties, such as micronfine fiber, modified cross-section yarns, blended filament yarns different in shrinkage and the like or by a combination thereof. The texture and the feeling peculiar to synthetic fibers which are not observed in natural fibers, in a silk-like fabric, a thin raised textured fabric (peach skin), a rayon-like fabric and the like, have been accepted, and they have been rapidly widened on the market.
However, in the dyeing of these composite materials, there are problems caused by microfine fibers. For example, the following problems tend to occur.
(1) A reflected light on a fiber surface is increased to decrease a visual density of a dyed product. Accordingly, in order to obtain the same surface density of the dyed product as that of the conventional product, a higher color value is required. (A color value is in parallel with a surface area.)
(2) A dyed product is liable to undergo oxidation and reduction with light, and a fastness to light of a dyed product is decreased.
(3) Due to (1), an amount of a dye used for a unit area is increased, so that a fastness to sublimation and a fastness to wetting of a dyed product are decreased.
(4) An unevenness (non-level dyeing) of a dyed product occurs owing to a difference in a thickness of composite fibers.
Further, finishing of a ceremonial dress, namely, a formal wear with a black dye is taken up as one of finishings which have been widely conducted in recent years. With respect to the dyeing in this field, a color of a dyed product has been required to be as deep black as possible, and various studies have been conducted. For example, there are improvements such as a method for modifying fibers themselves in which pores are formed in advance in a surface of a fiber, a finishing method in which a resin film having a low refractive index is formed on a surface of a fiber (darkening of a color) and the like, and the development of a new dye that gives a deep black color. With respect to the dye in these, it is required that a deep black color is given and a color deviation which is caused when a light source changes is low, that is, a so-called color rendering property is low.
In order to solve these problems, not only is it required to use a dye which is superior in a fastness and a build-up property, but also it is required to develop and use a dye which is excellent in a level dyeing property and a solid property of a fabric formed of composite yarns different in the thickness. Especially, for obtaining a dyed product with a dark blue or black color, a high build-up property is required, and a color value which is from 2 to 5 times that of a general color is needed. Besides, in a ceremonial dress, it has been considered good that a color of a dyed product is as deep as possible and a noble black color is given. Further, a change in color (color deviation) of a dyed product which is caused by change of a light source is termed a color rendering property. Generally, in a black dyed product, this color deviation tends to occur. In this instance, a change in color is problematic in many cases under a standard light source A typified by a tungsten light source to a color under a standard light source D65 or the like. The reason is that a relative spectral distribution of a blackbody such as a tungsten bulb or the like is extremely different to a standard light source D65 or the like, which results in a great change in color. For example, spotlights that are often used in hotels, wedding halls or the like are given by tungsten bulbs in many cases. When the spotlights are illuminated, a phenomenon occurs that a dress which must be dark black appears extremely reddish.
As a method for improving such a color deviation (color rendering property), a method for dyeing with a dye composition containing a compound which has absorption at from 650 to 800 nm is proposed in JP-A-Shou 62-246964, JP-A-Shou 62-246965, JP-A-Hei 5-18955, JP-A-Hei 1-28456 and the like. However, the so far developed compounds having absorption in the long wavelength (or near infrared) are not satisfactory with respect to both the effect of improving the color rendering property and the economics.
The present inventors have assiduously conducted investigations to solve the problems, and have consequently found that the problems are solved by conducting dyeing with a dye composition containing a disperse dye having a specific structure. This finding has led to the completion of the invention.